. >> reporter: he hasn't recovered, and a joint investigation by abc news and the food & environment reporting network found more than 100 reported illnesses due to blue/green algae exposure. >> essentially if we don't solve this problem, somebody's going to die. >> reporter: ohio state's dr. jeffrey reuter is the foremost authority on blue/green algae. he says it's a nationwide problem caused by farm fertilizer runoff. the cure, he says, is convincing farmers to carefully fertilize so nutrients stay on the fields and not in the water. >> otherwise these blooms are going to continue to grow. the human health problems that we see are going to increase. >> reporter: assaulting our senses, our economy, and our health. jim avila, abc news, lake petenwell, wisconsin. >> that is nasty stuff. >> oh, that's an understand statement, but the wisconsin department of natural resources says the best way to treat this is naturally, but they say it could take several years to get rid of it completely. in fact, there was a large amount of -- lake erie, almost a third of the surface, covered. >> cut